However, where the apparatus to be assembled becomes too large for this space, problems do arise. Of course, the height between the working deck and the intermediate deck can be increased, though this will be at the expense of the stability of the ship. It is known that to solve this problem a blow-out preventor for example, is assembled in two separate parts, then the two parts moved to the centre above the opening, coupling them up, testing and then lowering through the opening. These operations are very time consuming and meanwhile no further drilling can be done. Furthermore, the working deck has to be constructed in such a way as to allow the turntable to be removed, to enable the top part of the blow-out preventor to protrude through.
It is also known to provide the working deck with a slot. The blow-out preventor, assembled and tested, located on the intermediate deck, protrudes upwards through this slot and has to be moved sideways in order to bring it above the opening. This cuts down the loss of time, but the working deck has to be fitted with removable parts and consequently becomes complicated and expensive.